Putter heads

ABSTRACT

A putter-head ( 1 ) giving positive ball-topspin (S) for impact-heights (h i ) above 5 mm from its sole ( 6 ), has its center of mass ( 9 ) located p mm behind its impact face ( 8 ) at height h c  mm above the sole ( 6 ), a mass M kgm and a radius of gyration K mm about the heel-toe axis ( 4 - 5 ) through the center of mass ( 9 ). The loft (α) of the impact face ( 8 ) increases monotonically with height from 5 to 15 mm above the sole ( 6 ), where (K 2 /p) is greater than 5 mm and S=S G +S L  where S G  and S L  are percentage spin rates based on: 
 
 S   G =(250× h )/[(3.2+70× M )×( K   2   /p )+ p] 
 
 S   L =(−0.76×α i )/[1+0.04×( p/K)   2 ]
 
for which:  h=h   i   −h   c   −p ×sin( a   i ) 
 
     and α i  degrees is impact-face loft at height h i .  
     From the sole ( 6 ) upwards, the impact face curves ( 16 ) from negative- to positive-loft and merges into an upper flat-portion ( 15 ) of positive loft. Alternatively, it has upper and lower flat-portions ( 21, 22 ) of positive- and negative-loft respectively. A hosel ( 30, 31 ) gives high compliance at impact for head-rotation relative to the shaft ( 33 ) about the heel-toe axis ( 4 - 5 ), and allows choice of lie in shaft-attachment.

This invention relates to putter-heads and is concerned especially withputter-heads for imparting topspin to a golf ball at impact.

In putting a golf ball, it is desirable to impart forward rolling spinor topspin to the ball during the putting stroke. Topspin reduces ballskid on the putting surface and helps to initiate pure rolling motion.Imparted topspin is defined as the component of ball spin about ahorizontal axis parallel to the putter impact-face imparted at impact bya putter such that the ball peripheral speed on the top surface of theball exceeds its linear or translational speed.

It is known that putters with negative face-loft normally hit above thehorizontal equator of a golf ball and thus tend to impart topspin.However, this type of impact disadvantageously forces the ball downwardsand into the putting surface, causing erratic loss of launch energy,especially on soft putting greens.

Thus, it is preferable that the impact point on the ball is below itsequator, which generally ensures that the ball lifts off the puttingsurface at impact. Impacts just above the horizontal equator of the ballare also acceptable, especially if combined with an upward putter-headtrajectory as this ensures that the downward component of impact forceis a small fraction of the total and so has negligibledeleterious-effect on the putt.

It is one of the objects of the present invention to provide an improvedputter-head for imparting topspin to a golf ball at impact.

According to the present invention there is provided a putter-head forimparting a positive rate (S) of topspin on a golf ball for impacts withthe ball throughout a range of impact height (h_(i)) extending above 5millimetre from the bottom of the putter-head, wherein the head has acentre of mass located at a distance p millimetre behind its impact faceand a height h_(c) millimetre above the bottom of the head, a mass Mkilogram and a radius of gyration K millimetre about the heel-toe axisthrough the centre of mass, and the loft (a) of the impact faceincreases monotonically with height from 5 to 15 millimetre above thebottom of the putter-head, and wherein:K ² /p>5   (a)andS=S _(G) +S _(L)   (b)

where the spin rates S_(G) and S_(L) expressed as percentages, are asfollows:S _(G)=(250×h)/[(3.2+70×M)×(K ² /p)+p]S _(L)=(−0.76×α_(i))/[1+0.04×(p/K)²]for which:h=h _(i) −h _(c) −p×sin(α_(i))

and

α_(i) degrees is the impact-face loft at height h_(i) millimetre.

The loft (α₁₅) at 15 millimetre above the bottom of the head may be atleast 3 degrees larger than the loft (α₅) at 5 millimetre above thebottom of the head, but is preferably at least 5 degrees or moreespecially, 7 degrees, larger.

The minimum value of rate S of topspin may be at least +2.5% or, morepreferably, +5.0% for values of h_(i) above 5 millimetre from the bottomof the putter-head. For values of h_(i) down to 2.5 millimetre, theminimum spin rate S is preferably +5.0%. For preference, the heighth_(c) may be less than 10 millimetre, or, more preferably, not more than7 millimetre, and the value of (K²/p) may for preference be not lessthan 5 or, more especially, 8 millimetre. The distance p is preferablyat least 10 millimetre and less than 35 millimetre but more preferablyless than 30 millimetre.

For preference a putter-head according to the invention is provided withshaft attachment means that provides additional compliance to rotationof the head of up to ±0.5 degrees relative to the shaft to enableachievement of vertical gear effect. Head rotation about the heel-toeaxis may also be increased by arranging that stiffness of the shaftwhere it attaches to the putter-head is minimised. This is achieved byensuring that the shaft deformation during impact is predominately inbending or twisting mode rather than in axial compression or elongationmode. Thus for preference, a putter-head according to the invention maybe provided with shaft attachment means wherein the axis of theshaft-attachment means is horizontally displaced d millimetre eitherside of the horizontal heel-toe axis through the centre of mass. Tooptimise the imparted topspin properties of the assembled putter, dshould be ideally zero or less than r, where r is the radius of theputter shaft at the shaft-attachment means. It is also advantageous forthe horizontal displacement (measured in any direction) of theshaft-attachment means from the centre of mass of the putter-head to beless than the radius of gyration K. Putter-heads in accordance with thepresent invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIGS. 1 to 3 are front-elevation, rear-elevation and plan viewrespectively of a first putter-head according to the invention;

FIG. 4 is a sectional side-elevation of the first putter-head taken onthe line IV-IV of FIG. 3;

FIG. 5 is a perspective view from the rear of the first putter-head;

FIGS. 6 a and 6 b are, respectively, diagrammatic views of the centresection of the first putter-head and a golf ball at impact, in twodifferent circumstances;

FIG. 7 is a sectional side-elevation of a second putter-head accordingto the invention;

FIG. 8 is illustrative of a form of hosel that may be used in theputter-heads of FIGS. 1 to 5 and FIG. 7;

FIGS. 9 a and 9 b are, respectively, sectional views of use of the hoselof FIG. 8 in providing two different angles of lie of the putter-shaft;and

FIG. 10 is in further illustration of a feature of the hosel of FIG. 8.

Referring to FIGS. 1 to 5, the putter-head 1, comprises an impact-faceflange 2 and a base 3. The base 3, which forms the major part of theputter-head 1, defines the heel 4, the toe 5 and the sole 6 of the head1, and incorporates a shaft-hosel 7. The flange 2 is of an unusuallythin section for a putter-head, being for example of 4 millimetre orless in thickness, yet establishes a rigid interface between the impactface 8 and the base 3. This rigidity is important in ensuring thatimpacts on the middle or upper part of the face 8 do not deflect theflange 2 relative to the base 3, but instead rotate the entire head 1fully about its centre of mass 9. This in turn ensures that theputter-head 1 behaves as a rigid body during impact, and parameters suchas imparted ball spin and velocity are accurately predictable and fullyachieved.

In one construction of the putter-head 1 of FIGS. 1 to 5, the desiredrigidity and mass properties are realised by casting it of 316 stainlesssteel or a similar alloy. In an alternative construction, the impactflange 2 is provided as a separate part of titanium, aluminium ormagnesium alloy or of a high modulus composite. The main requirement isthat the flange 2 has a mass which is a small proportion of the overallmass of the putter-head 1, yet provides a rigid interface between thegolf ball and the base 3 at impact. This allows-the centre of mass 9 tobe positioned close to the bottom surface or sole 6, and some distancefrom the face 8. The height h, of centre of mass 9 above the sole 6 ispreferably less than 10 millimetre or, more preferably, not more than 7millimetre since this limits the amount of negative loft required.

A very high value of p, the distance of centre of mass 9 behind theimpact face 8, produces high sidespin and directional errors underoffset impacts. This undesirable characteristic can be reduced byincreasing the moment of inertia of the head 1 about the vertical axis,but increase of this moment affects playing control and/or requires themass of the head 1 to be excessive. As a result, it is preferable tolimit the distance p to be less than 35 millimetre, but, morepreferably, less than 30 millimetre. Small values of p aredisadvantageous in putter-heads of the present invention since theyseverely limit vertical gear effect, and accordingly, it is preferred toadopt a construction for which p is at least 10 millimetre.

By way of modification of the putter-head of FIGS. 1 to 5, the impactface 8 may be formed by material which is softer than that of the flange2 and which is provided as a layer, or as an insert, bonded to theflange 2 for reducing vibration and noise intensity (so as to give aso-called ‘soft-feel’). However, it is disadvantageous to have theentire structure of the flange 2 in soft material as this reducestopspin imparted by vertical gear-effect.

The putter-head of FIGS. 1 to 5 and its action will now be described infurther detail with reference to FIGS. 6 a and 6 b which are,respectively, diagrammatic representations of the centre section of theputter-head 1 at the instant of impact with a golf ball 13 resting on aputting surface 14, in two different circumstances.

As illustrated in exaggerated form in FIGS. 6 a and 6 b, the impact face8 of the putter-head 1 is of curved profile transversely of the heel-toeaxis only, and has a lower, curved half 15 that has a loft angle αdegrees which increases with increase in height, progressively from anegative value at the sole 6, through zero to a positive value α_(MAX)where it merges into the upper half 16 of the face 8. The upper half 16is flat and has a loft angle of α_(MAX) so as to be tangential to thelower half 15 where they merge; accordingly, the loft of the impact face8 increases monotonically throughout its full height upwardly from thesole 6.

As represented only in FIG. 6 a, the centre of mass 9 of the putter-head1 is located at distance p millimetre behind the impact face 8 and at aheight h_(c) millimetre above the sole 6. The centre of impact of theface 8 with the ball 13 (which is a playing variable with random error)is shown as occurring at height ha above the sole 6 in the circumstancesof FIG. 6 a but at height h_(b) in the circumstances of FIG. 6 b.

The main effect required of the impact is to launch the golf ball 13with linear velocity substantially along the intended line of putt andpreferably with a slight positive (upward) elevation angle. The upwardtrajectory is often provided by a small amount of loft (typically +3degrees) on the impact-face of a putter. Moreover, most golfers adopt anapproximate ‘pendulum swing’ in putting, in which the putter-head isswung about a substantially horizontal axis with the swing rotation axisand the putter shaft axis in (or nearly so) a common plane that issubstantially parallel to the heel-toe axis of the putter-head. The mainvariable with this type of swing is the position of the ball in relationto the vertical arc followed by the putter-head. For preference, impactwith the ball occurs at or just beyond the bottom of the arc (on theupward part of the arc), but in practice may occur before or later thanthis.

In the circumstances represented in FIG. 6 a, impact takes place at thebottom of the arc, where the putter-head trajectory is horizontal (shownby arrow 17 a). Impact in such circumstances generally occurs atmid-height, within the upper part 15 of the impact face 8. The loftangle α_(MAX) applies provided the clearance 18 a between the puttingsurface 14 and the sole 6 is not more than the radius of the ball 13less the height of the curved lower half 16 of the impact face 8. If theground-to-sole clearance 18 a is more than this, the height of contactwill increase and may disadvantageously rise above the horizontalequator of the ball 13 and consequently launch the ball 13 with a slightnegative elevation trajectory. This type of putting stroke is rareexcept with players of less than moderate skill and typifies poor puttercontrol. Nevertheless it is preferred that excessive negative balltrajectory is avoided by providing that the region on the impact-facewhere the loft is negative is limited to the lower 12 millimetre, ormore preferably the lower 9 millimetre.

FIG. 6 b represents the circumstances in which impact occurs at a pointbeyond the bottom of the pendulum arc where the putter-head trajectory(depicted by arrow 17 b) has positive elevation. The ball launchtrajectory in these circumstances is dependent on the combination oftrajectory elevation angle and the loft angle at impact; the latter isgenerally slightly negative and varies both with the ground clearance 18b and the elevation angle of the trajectory 17 b. Provided the sum ofputter-head trajectory angle and loft angle at impact point is greaterthan −20% of the trajectory elevation angle, the ball launch elevationangle will be positive.

Thus, the ball is still given a slight lift for impacts in the lower(negative loft) region of the impact-face 8 provided the bottom of thependulum arc is kept low as before.

The aim of the present invention is to provide a putter-head thatimparts topspin on the ball from all pendulum-swing putts but alsoprovides high probability of imparting positive lift on the ball atimpact.

It is known that two mechanisms impart spin with club-on-ball impact ingolf, namely eccentric impact, commonly known as ‘gear-effect’, andoblique impact which is most commonly experienced as backspin due toclub-face loft. The gear-effect realised with a putter-head is dependenton the condition that the line of impact (that is, the line normal tothe impact surfaces at the point of impact) is offset from the centre ofmass of the head. It follows that the condition for gear-effect with theputter-head of the present invention is also dependent on the loft angleof the impact face at the point of impact.

The offset distance h between the line of impact and the centre of mass9 is given by:h=h _(i) −h _(c) −p×sin(α_(i))   (1)

where h_(c) and h_(i) are, respectively, the height (millimetre) of thecentre of mass 9 and the impact point above the bottom-most part, thesole 6, of the putter-head, and α_(i) (degrees) is the loft angle of theputter face 8 at the point of impact (positive for upward tilt).

The value of spin attainable with gear-effect is known from Newtoniandynamics assuming that the putter-head and golf ball behave as freerigid bodies at impact, and is given, as a percentage, by:S _(G)=(250×h)/[(3.2+70×M)×(K ² /p)+p]  (2)where M is the putter-head mass (kilogram), K is the radius of gyrationfor rotation about the horizontal heel-toe axis through the centre ofmass (millimetre) and S_(G) is the ratio (expressed as a percentage) ofthe peripheral velocity of the ball due to rotation, to its linear ortranslational velocity.

It is found that S_(G) is highly dependent on the term (K²/p) inequation (2). A low value of this term, such as 5 (millimetre) gives avery high vertical gear effect, which in turn requires high negativeloft to overcome the tendency for backspin at low impact heights. It isalso the case that most conventional putter-heads (especially low cost,one-piece cast heads) have values of (K²/p) of 10 to 20 or so, andgolfers are familiar and more attuned to this weight distribution. It isthus an aim with the putter-head of the invention to arrange that (K²/p)is at least more than 5 millimetre, but preferably 8 millimetres ormore.

Further, golfers are not used to putters having very low inertia aboutthe heel-toe axis (or about any other axis). Such low-inertia putterscan feel less ‘solid’ to play with, which is disadvantageous.

It is accordingly preferable that the value of the heel-toe inertia,namely, (M×K²), is not less than 25 kilogram-millimetres² or, morepreferably, is greater than 30 kilogram-millimetres².

For vertical gear effect to impart topspin rather than backspin, thevalue of h must be positive. This is exemplified in FIG. 6 a where theline of impact 19 a (collinear with the centre of the ball 13 and theimpact point) passes above the centre of mass 9.

With pendulum-swing putts the putter-head elevation trajectory is alwaysparallel to the sole 6 and therefore the spin imparted due to obliqueimpact is a function of the impact-face loft α_(i) but not trajectory,and is given by:S _(L)=(−0.76×α_(i))/[1+0.04×(p/K)²]

where S_(L) denotes the spin ratio (expressed as a percentage anddefined as for S_(G)) as a function of loft. It is to be noted thatpositive loft imparts negative spin or backspin and negative loftimparts topspin.

Conveniently, it is practical to provide negative loft, which in turnimparts topspin, in the lower half 16 of the impact-face 8 and thiscompensates for the fact that the height h defined in equation (1)normally becomes negative for small values of hi. This is depicted inFIG. 6 b where the line of impact 19 b is shown to pass below the centreof mass 9.

The value of height h can in practice be kept positive even for zeroimpact-height h_(i) by arranging that:h_(c)−p×sin(α_(i))

remains positive. However, this option requires severely negative loft,especially for smaller values of distance p and thus undesirably impartsnegative ball-launch trajectory rather than the desired lift. It is thusmuch more preferable to arrange that the sum of S_(L) and S_(G) ispositive at least for putts above the lower limit of useful impactheight, for example above 5 millimetres or 2.5 millimetres. It ispreferable that the minimum spin rate is +2.5%, or more preferably+5.0%, above 5 millimetres, but below this down to 2.5 millimetres, itis very desirably +5.0%.

Since the diameter of the impact footprint (that is, the contactdeformation area) is usually at least 5 millimetres (except for verylow-velocity putts), impacts at heights below 2.5 millimetres encroachonto the lower lip of the impact face. In these circumstances, an impactwill ‘top’ the ball, giving abundant topspin but at the expense oferratic length and direction control.

It can be seen from equations (1) to (3) that a number of putter-headparameters determine spin rate, namely p, h_(c), M, K and α_(i) (whichis a function of impact height). Typical value ranges of theseparameters for blade-style putters according to the invention, are givenin Table I. TABLE I p 10 to 18 millimetres h_(c) 6 to 10 millimetres M0.31 to 0.36 kilogram K 10 to 13 millimetres

For mallet-style putters the values for distance p and radius ofgyration K are generally larger than those for blade-style putters.Table II below gives an example of a putter-head based on FIGS. 1 to 5.TABLE II h_(i) α_(i) S_(G) S_(L) S_(G) + S_(L) (mm) (deg) (%) (%) (%)2.5 −7.5 −2.4 +5.3 +2.9 5 −5.0 −0.5 +3.5 +3.0 12 +2.0 4.9 −1.4 +3.5p = 16 millimetresh_(c) = 6.8 millimetresM = 0.32 kilogramK = 11.6 millimetresα_(MAX) = 2.0 degrees (h_(i) > 12 millimetres)

It is found in practice that the position of the shaft hosel 7 has astrong influence on the putter-head rotation about the heel-toe axisduring the very short duration of impact (less than one millisecond). Ithas been found experimentally that if distance d is the horizontaloffset between the shaft attachment axis and the heel-toe axis, topspinperformance is enhanced when d is zero and that increasing d reduces theimparted topspin. In order to optimise the imparted topspin propertiesof the assembled putter, d should be ideally zero, or, more generally,less than the radius r of the putter-shaft.

A further advantage of positioning the shaft coupling close to thecentre of mass of the putter-head is that shaft vibrations due toeccentric impact are minimised. In this respect, it is advantageous thatthe axis of the means for attachment of the shaft passes close(preferably not more than K millimetres) to the centre of mass of theputter-head (as distinct from the heel-toe axis through this centre).

FIG. 7 shows a sectional side-elevation of a putter-head 20 that isgenerally the same as the putter-head of FIGS. 1 to 5 except that theimpact face in this case comprises an upper, flat-face portion 21 and alower, flat-face portion 22. The upper portion 21 has typically zero orpositive loft whereas the lower portion 22 has negative loft;differences in loft-are exaggerated in FIG. 7. The upper and lowerportions 21 and 22 join one another in a horizontal junction 23 (whichis parallel to the heel-toe axis and thus normal to the plane of FIG.7). The loft angle of the impact face accordingly changes abruptly atthe junction 23, but the effective loft actually experienced for impactson or near the junction 23 changes only gradually as the point of impactis moved through the junction 23, owing to the softness of the covermaterial of the ball. More particularly, the softness results in theimpact force being distributed above and below the junction 23 with theresult that the effective loft tends to a value intermediate the loftsof the two flat-face portions 21 and 22; the junction 23 can bechamfered or rounded to enhance the distribution. The change in loft mayalso be made more gradual by reducing the hardness of the impactsurface, for example by using an elastomer insert instead of a steelface as depicted in FIG. 7.

FIG. 8 shows a sectional view of an alternative form of hosel involvinga male stub 30 and an annular recess 31 concentric with it. The axis 32of stub 30 is inclined at the desired lie angle relative to thehorizontal for attachment of the putter-shaft. Attachment of the shaftis carried out by applying a thixotropic adhesive within the hollow tipof the shaft and then placing the shaft-tip over the stub 30 to locatewithin the surrounding annular recess 31; the adhesive desirably hasgood gap-filling properties and may, for example, be the ‘E3332’ epoxyadhesive sold under the registered trade mark PERMABOND. The recess 31is typically only 2 to 3 millimetres deep and serves to centre theshaft-tip relative to the stub 30.

The dimensions of the stub 30 and recess 31 are such that the shaft canbe fitted at different angles relative to the concentric position so asto allow for different lie preferences. This is illustrated by FIGS. 9 aand 9 b, FIG. 9 a showing adoption of an ‘upright’ lie for shaft 33 onthe stub 30 in which the shaft 33 is inclined at an angle of 78 degreesto the horizontal. FIG. 9 b on the other hand, shows adoption of a‘flat’ lie in which the shaft 33 is inclined at an angle of 66 degreesto the horizontal.

Referring again to FIG. 8, the seating plane at the bottom of theannular recess 31 is shown by dashed line 34, and intentionally notsquare to the axis 32 but is instead tilted towards the horizontal sothat the tip of the shaft 33 rests on nominally one point on the planecontaining line 34. This arrangement is shown more clearly in FIG. 10where the tip of shaft 33 touches line 34 at only one point 35. It isarranged that this point 35 is located on the heel-toe axis 36.

At impact, the putter-head rotates about the heel-toe axis 36. Thisarrangement provides very high compliance to putter-head rotationrelative to the shaft 33 about the heel-toe axis 36 since the rim of theshaft 33 is decoupled from the putter-head body via the cured adhesivematerial of relatively low modulus, and the only direct contact with theputter-head is at the one point 35 on the axis 34 of rotation.

1-20. (canceled)
 21. A putter-head for imparting a positive rate (S) oftopspin on a golf ball for impacts with the ball throughout a range ofimpact height (h_(i)) extending above 5 millimeter from the bottom ofthe putter-head, wherein the head has a center of mass located at adistance p millimeter behind its impact face and a height h_(c)millimeter above the bottom of the head, a mass M kilogram and a radiusof gyration K millimeter about the heel-toe axis through the center ofmass, and the loft (α) of the impact face increases monotonically withheight from 5 to 15 millimeter above the bottom of the putter-head, andwherein:K ² /p>5   (a)andS=S _(G) +S _(L)   (b) where the spin rates S_(G) and S_(L) expressed aspercentages, are as follows:S _(G)=(250×h)/[(3.2+70×m)×(K ² /p)+p]S _(L)=(−0.76×α_(i))/[1+0.04×(p/K)²]for which:h=h _(i) −h _(c) −p×sin(α_(i)) and α_(i) degrees is the impact-face loftat height h_(i) millimeter.
 22. The putter-head according to claim 21,wherein the loft (α₁₅) at 15 millimeter above the bottom of the head isat least 3 degrees larger than the loft (α₅) at 5 millimeter above thebottom of the head.
 23. The putter-head according to claim 22, whereinα₁₅ is at least 5 degrees larger than α₅.
 24. The putter-head accordingto claim 23, wherein α₁₅ is at least 7 degrees larger than α₅.
 25. Theputter-head according to claim 21, wherein S is at least +2.5%.
 26. Theputter-head according to claim 25, wherein S is at least +5.0%.
 27. Theputter-head according to claim 21, wherein the head also imparts apositive rate (S) of topspin of at least 5.0% for impacts with the ballthroughout a range of impact height (h_(i)) extending above 2.5millimeter from the bottom of the putter-head.
 28. The putter-headaccording to claim 21, wherein h_(c) is less than 10 millimeter.
 29. Theputter-head according to claim 28, wherein h_(c) is not more than 7millimeter.
 30. The putter-head according to claim 21, wherein the ratioK²/p is more than 5 millimeter.
 31. The putter-head according to claim30, wherein the ratio K²/p is not less than 8 millimeter.
 32. Theputter-head according to claim 31, wherein p is at least 10 millimeter.33. The putter-head according to claim 32, wherein p is less than 35millimeter.
 34. The putter-head according to claim 33, wherein p is lessthan 30 millimeter.
 35. The putter-head according to claim 21, includingshaft-attachment means and wherein a putter-shaft is attached to thehead via the shaft-attachment means and the horizontal offset of theaxis of the shaft from the heel-toe axis is less than the radius of theshaft at the shaft-attachment means.
 36. The putter-head according toclaim 35, wherein the shaft-attachment means has zero horizontal offsetfrom the heel-toe axis.
 37. The putter-head according to claim 35,wherein the horizontal displacement of the shaft-attachment means fromthe center of mass is less than the radius of gyration K.
 38. Theputter-head according to claim 21, wherein the impact face includes anupper, flat portion having positive loft.
 39. The putter-head accordingto claim 21, wherein the impact face includes a lower portion which iscurved and has loft that increases from a negative value to a positivevalue upwardly from the bottom of the head.
 40. The putter-headaccording to claim 21, wherein the impact face includes a lower, flatportion having negative loft.